Capture event id in page load

During pageload i would like capture, which event is raised and its ID .e.g button click event , textbox value change event.  I have tried by using the below code in page load but always iam getting only balnk value.kindly help me.

Dim lsTarget As String
lsTarget = Request.Form("__EVENTTARGET").ToString
lsTarget = Request.Form("__EVENTARGS")


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